1530s, "to poke with a stick," of uncertain origin; possibly [Barnhart, Century Dictionary] a variant of brod, from Middle English brodden "to goad," from Old Norse broddr "shaft, spike" (see brad), or perhaps imitative [OED]. Compare dialectal prog "pointed instrument for poking" (1610s), also as a verb, "to poke about."
Figurative sense of "mental incitement or instigation" is by 1871. Related: Prodded; prodding.
1787, "pointed or blunt-pointed instrument used in prodding;" 1802, "act of prodding;" from prod (v.). A provincial word; it also meant "long wooden pin used to secure thatch on a roof."